Added a cancelling function that can be used after some time has passed.

[o-jasper]

As discussed(a little) Also added some tests. The amount of time that has to pass is based on a set-date compiled-in.

Also there are more stop('hammer time') and assert self.stopped == 'hammer time' statements, in part they're redundant, of course.

[jorisbontje]

Thanks! Merged (with a little cleanup)

[o-jasper]

Yaay (checked the cleanup for my information)